Process for hardening metals



Patented Sept. 25, 1934 UNITED STATES PATENT OFFICE to Bennett-Chapmanizing, Inc.,

Springfield,

Masa, a. corporation 01' Massachusetts No Drawing. Application August 20, 1931, Serial No. 558,417

'7 Claims.

My invention relates to the art of casehardening metals and it particularly has for an object to provide a method whereby the metal may be hardened at low temperatures in much 5 shorter time than is now required for methods for low temperature hardening now in use.

Another object of the invention is to provide a method for low temperature hardening which is applicable to ferrous metals having a wide range of analyses.

Another object of the invention is to provide a method for low temperature hardening which does not require a special alloy suchas aluminum, chrome, molybdenum, vanadium, etc. in the metal to be treated.

Further it is an object of my invention to introduce a nitrogen bearing gas below the surface of a heated bath of carbon and nitrogen bearing salts, thereby energizing the bath with a continuous flow of hydrogen and nitrogen, the nitrogen permeating the entire bath and the hydrogen passing upward to the surface, at which point it ignites with the oxygen of the air.

Generically the invention resides in providing for the metal to be hardened, a bath of suitable material and energizing the bath and maintaining it at proper strength by the flow of a suitable gas introduced beneath the surface of the bath, the gas being such that its hardening agent will be absorbed by the materials of the bath at the temperature at which the bath is maintained.

The invention is applicable to a variety of metals and especially to the ferrous metals and alloys of same. For the purpose of exemplification, the present invention will be described more particularly as applied to the treatment of steel; it is to be understood, however, that the invention is not limited to use with steel, but contemplates use with any metal to which the method is applicable.

Other objects of the invention will become apparent as the description proceeds.

Stated broadly, the present invention includes the method of preparing a bath of suitable hard- 5 ening agent and introducing beneath the surface of the bath a flow of gas which will release a gaseous hardening agent at the bath temperature and thus energize and enrich the bath for the work it is desired to accomplish; then immersing the metal to be treated in the bath for the required time while maintaining the bath at the temperature required; then removing the metal from the bath and quenching it in a suitable liquid or atmosphere.

To obtain the maximum advantages and effectiveness of the present invention, the bath should be composed of materials which will become liquid at a low temperature and have the property of releasing a hardening agent to act on the metal immersed therein; cyanide salts have low melting points, and at low temperature will release the hardening agents, carbon and nitrogen, to act on metal therein immersed. The gas used to energize and enrich the molten bath should contain the hardening agent desired in the treatment and should have the property of releasing the hardening agent at the temperature of the bath, so that when the gas is introduced beneath the surface of the bath, its hardening agent will be immediately released and become absorbed by or incorporated with the material of the bath; ammonia contains the hardening agent, nitrogen, and will release same at a low temperature and therefore ammonia is a suitable gaseous agent to employ in the practice of the present invention in connection with a bath of molten cyanide salts.

It has heretofore been the practice in the hardening of ferrous metal using nitrogen as the hardening agent, to subject the metal, which must contain a percentage of aluminum, chrome, molybdenum, vanadium or other special alloy, to the action of ammonia gas, usually by heating the metal in a retort or closed furnace chamber while a current of ammonia gas flows through the retort or furnace chamber; the process is generally termed nitriding and requires much time, from ten to ninety hours, depending on the degree of hardness and the depth of penetration of same.

In the practice of the present invention for the hardening of ferrous metals, by use of which any ferrous metal regardless of alloy content may be treated, a molten bath of cyanide salts is prepared and maintained at a temperature from the molten state upward depending on the metal to be treated and the results desired; beneath the surface of the bath and preferably at or adjacent the bottom, is introduced a flow of ammonia gas for the purpose of continuously maintaining, energizing and enriching the nitrogen content of the bath, the hydrogen of the ammonia gas escaping from the bath upon its dissociation from the nitrogen by heat. .The metal to be treated is immersed in the bath for a period suflicient to obtain the desired hardness and depth of penetration, the time depending also on the size of the section being treated. When the metal has been immersed in the bath for the required time, it is removed therefrom 11 and quenched in suitable liquid or atmosphere.

From the foregoing description, it is thought the invention will be readily understood by those skilled in the art.

What I claim is:

l. The process of hardening ferrous metal which consists in immersing said metal in a molten bath of cyanide salts activated by a flow oi ammonia gas.

2. The process of hardening ferrous metal which consists in immersing said metal in a molten bath *of cyanide salts activated and energized by a flow of ammonia gas.

3. The process of hardening ferrous metal which consists in immersing said metal in a molten bath of cyanide salts having a flow of ammonia gas introduced beneath the surface of said bath.

4. The process of hardening ferrous metal which consists in preparing a molten bath of cyanide salts, introducing beneath the surface of said bath a flow of ammonia gas, immersing the metal to be treated in said bath while maintaining the bath at predetermined temperature,

removing the metal from said bath and quenching the metal in liquid or atmosphere.

5. The process of hardening ferrous metal which consists in preparing a bath of molten cyanide salts at a temperature from its molten state upwardly, immersing the metal in the bath and activating the bath by introducing ammonia gas into the molten bath and after the metal has been sumciently treated in the bath, removing the same from the bath and quenching it in a suitable medium.

6. The process ;of hardening ferrous metal which consists in immersing said metal in a molten bath of cyanide salts having a flow of ammonia gas introduced beneath the surface of said bath to agitate, activate and energize the bath.

7. The process of nitriding which comprises 77 NILBUR R. BENNETT.

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